Conventional print systems that incorporate a fuser portion often have image related defects that occur when subjecting a substrate to duplex printing. In duplex printing, a substrate having a first surface and a second surface has one or more images applied to each of the first surface and the second surface by one or more photoreceptors.
In a conventional print system, one or more images that are applied to one or more of the first surface and the second surface of a substrate are later fused to the substrate by the fuser portion. To fuse an image to a substrate, the fuser portion often comprises a fuser member, such as a fuser roll or belt, and a pressure member, such as a pressure roll or belt. The fuser member and the pressure member, together, form a fusing nip through which the substrate may pass for fusing the one or more images to the substrate. The substrate is under a pressure in the fusing nip because the fuser member and the pressure member are either in contact with one another in the fusing nip, or at least very close to one another in the fusing nip such that when the substrate passes through the fusing nip, a pressure is applied.
A release agent applicator in a conventional print system applies a layer of release agent to the fuser member, for example, to aid in stripping the sheeted substrate from the fuser member after the substrate passes through the fusing nip. The release agent may be, for example, an oil, lubricant, or other substance that reduces an adhesion that may occur between the substrate and the fuser member, The release agent applied to the fuser member often transfers to the surface of the substrate that contacts the fusing member.
If, for example, the substrate is a sheeted substrate, and a printing run applies images to more than one sheeted substrate, as a first sheeted substrate advances through the fuser portion of the printing system, there is often a gap between the first sheeted substrate and a second sheeted substrate. This gap continually occurs between any subsequent sheeted substrate and a substrate before it that may be processed by the print system during a print run of any number of sheets. This gap is commonly known as the inter-document zone.
When the inter-document zone occurs, i.e. there is no paper in the fusing nip, release agent often transfers to the pressure member from the fuser member. The release agent that transfers to the pressure member accumulates and/or transfers to the surface of a subsequent sheeted substrate that contacts the pressure member as the sheeted substrate passes through the fusing nip. For example, if the first surface of the substrate is in contact with the fuser member when passing through the fusing nip, the second surface of the substrate is in contact with the pressure member. While an image applied to the first surface is being fused to the first surface of the substrate, release agent is often transferred from the pressure member to the second surface of the substrate.
It is this transfer of release agent to the second surface of the substrate that causes image related defects in duplex printing modes. After the image is fused to the first surface of the substrate, the second surface of the substrate then has an image applied to it as well. Because the second surface of the substrate has release agent on it, this release agent is often transferred from the substrate to a photoreceptor belt that applies an image to the second surface of the substrate in duplex printing. The photoreceptor belt may be the same or a different photoreceptor belt as that which applies the image to the first surface of the substrate. Release agent build up on the photoreceptor belt may cause image related defects to either or both of the first surface and second surface images, depending on how the conventional print system is set up to conduct duplex printing, as release agent is continually transferred to the photoreceptor belt from the pressure member by way of the second surface of the substrate.